Phylogeography of Eastern Polynesian sandalwood (Santalum insulare), an endangered tree species from the Pacific: a study based on chloroplast microsatellites

Abstract

Aim Patterns of genetic variation within forest species are poorly documented in island ecosystems. The distribution of molecular variation for Santalum insulare, an endangered tree species endemic to the islands of eastern Polynesia, was analysed using chloroplast microsatellite markers. The aims were to quantify the genetic diversity; to assess the genetic structure; and to analyse the geographical distribution of the diversity within and between archipelagoes. The ultimate goal was to pre-define evolutionary significant units (ESUs) for conservation and restoration programmes of this species, which constitutes a natural resource on small, isolated islands.Location Eleven populations, each representative of one island, covering most of the natural occurrence of S. insulare were sampled: five populations from the Marquesas Archipelago; three from the Society Archipelago; and three from the Cook-Austral Archipelago. These South Pacific islands are known for their high degree of plant endemism, and for their human occupation by Polynesian migrations. The extensive exploitation of sandalwood by Europeans nearly 200 years ago for its fragrant heartwood, used overseas in incense, carving and essential oil production for perfume, has dramatically reduced the population size of this species.Methods We used chloroplast microsatellites, which provide useful information in phylogeographical forest tree analyses. They are maternally inherited in most angiosperms and present high polymorphism. Among the 499 individuals sampled, 345 were genotyped successfully. Classical models of population genetics were used to assess diversity parameters and phylogenetic relationships between populations.Results Four microsatellite primers showed 16 alleles and their combinations provided 17 chlorotypes, of which four exhibited a frequency > 10% in the total population. The gene diversity index was high for the total population (H e ¼ 0.82) and varied among archipelagoes from H e ¼ 0.40 to 0.67. Genetic structure is characterized by high levels of differentiation between archipelagoes (36% of total variation) and between islands, but differentiation between islands varied according to archipelago. The relationship between genetic and geographical distance confirms the low gene flow between archipelagoes. The minimum spanning tree of chlorotypes exhibits three clusters corresponding to the geographical distribution in the three main archipelagoes. Main conclusionsThe high level of diversity within the species was explained by an ancient presence on and around the hotspot traces currently occupied by young islands. Diversity in the species has enabled survival in a range of habitats.

Molecular phylogeography of the Society Islands (Tahiti; South Pacific) reveals departures from hotspot archipelago models

“…This represents the largest interisland distance in the Societies (150 km between Huahine and Moorea), and consequently an important role for allopatry in the diversification of the Societies biota. This pattern is seen in a number of animal taxa, including Misumenops crab spiders (Garb & Gillespie, , ), the two older Epicephala lineages (Hembry et al ., ), Pseudoloxops plant bugs (Balukjian, ), Rhyncogonus weevils (Claridge, ), Todiramphus kingfishers (Andersen et al ., ), the sandalwood Santalum insulare (Butaud et al ., ) and probably also the Grey‐green Fruit Dove Ptilinopus purpuratus (Cibois et al ., ). Acrocephalus reed warblers may also be consistent with this pattern as well (Cibois et al ., , ).…”

Sandalwood

“…S. lanceolatum is being trialed in Queensland (Bristow et al, 2000), while a concerted effort to reestablish S. austrocaledonicum as a tree crop is also underway in Vanuatu (Tate et al, 2006). S. insulare from eastern Polynesia is critically endangered due to overharvesting, and as such a conservation program is being implemented (Butaud et al, 2005).…”

“…insulare, a sandalwood growing throughout the French Polynesia was studied intensively by chloroplast microsatellite polymorphisms (Butaud et al, 2005). As populations of S. insulare are restricted to islands, gene flow between populations was particularly low.…”

Taxonomic Revision of the Endangered Hawaiian Red-flowered Sandalwoods (<I>Santalum</I>) and Discovery of an Ancient Hybrid Species

“…A. DC. ( Lhuillier et al 2006b ), as well as one cpDNAmicrosatellite (NTCP9; Bryan et al 1999 ;Butaud et al 2005 ). Amplifications were performed in a 10 μL volume [1 μL 10 × buffer (Applied Biosystems), 1 μL 10 μM dNTPs, 0.6 μL MgCl 2 , 0.1 μL Taq DNA polymerase (Applied Biosystems), 0.5 μL of each primer (forward and reverse), and 1 μL DNA template] using a PT-100 thermal cycler (MJ Research, Waltham Massachusetts) under the following polymerase chain reaction (PCR) parameters: 94°C for 5 min followed by 30 cycles of 92°C for 45 sec, annealing temperature ( Lhuillier et al 2006b ) for 45 sec, and 72°C for 1 min.…”

“…Therefore in this study, in addition to an expanded phylogenetic analysis based on nrDNA (ITS, ETS) and cpDNA (3′ trnK intron) sequences, evidence is integrated from two novel sources including a Bayesian STRUCTURE analysis using microsatellites, as well as a morphological analysis of 28 quantitative and qualitative characters. Microsatellite data have been chosen for the present study because they have high mutation rates and polymorphism, and are good to determine population genetic diversity and structure in taxa that have recently diverged, such as in island archipelagos ( Zhang and Hewitt 2003 ;Butaud et al 2005 ;Lhuillier et al 2006a ).…”